Method of strengthening glass articles

Abstract

This invention relates to a process for strengthening glass articles immediately after their formation and prior to annealing to remove stresses, and more specifically to increasing the strength of glass containers in terms of internal pressure retention as well as in thermal shock and impact resistance. The process involves allowing the newly-formed glass containers to cool down to a limited extent immediately subsequent to their formation, subjecting the defect-bearing exterior surfaces of the glass containers, which contain surface checks or cracks, to an elevated temperature for a brief period of time to physically alter the crack geometry of the defects and partially heal the same, and then annealing the glass containers to remove stresses therefrom. The glass containers then exhibit a strengthening of at least 10 to 20 percent, and in some cases as much as a 50 percent increase over their average untreated strength based on internal pressure strength tests which are indicative of overall strengthening of glass surfaces.

I claim: 
     
       1. The method of strengthening newly-formed glass articles having surface defects in their exterior surfaces comprising the steps of allowing the said newly-formed glass articles to partially cool immediately following their formation, immediately rapidly heating the defect-containing newly-formed exterior surfaces of said articles to an elevated temperature ranging from about 1000° to 1250° F. for a period of time ranging from about 1 second to about 6 minutes, depending upon selection of the heat source, said time period being less than that which would cause visible softening or fusing of the said exterior surfaces, and then annealing said glass articles to remove stresses therefrom. 
     
     
       2. The method in accordance with claim 1, wherein the geometry of the surface defects in said exterior surfaces is altered by such rapid heating. 
     
     
       3. The method in accordance with claim 1, wherein the said surface defects in said exterior surfaces are subjected to direct flame from a torch for a period of from about 1 to 10 seconds. 
     
     
       4. The method in accordance with claim 1, wherein the said glass articles are passed through an oven for subjection to the elevated temperature for a period of from 1 to 6 minutes. 
     
     
       5. The method in accordance with claim 1, wherein the said glass articles are strengthened ranging from about 10 to 50 percent or more than their original strength as indicated by internal pressure strength tests. 
     
     
       6. The method in accordance with claim 1, wherein at least some of the said surface defects in said exterior surfaces remain visible after treatment but are considerably strengthened due to a geometry change. 
     
     
       7. The method in accordance with claim 1, wherein the said surface defects in said exterior surfaces are subjected to an elevated temperature of about 1200° F. for a period of about 4 seconds. 
     
     
       8. The method in accordance with claim 1, wherein said glass articles comprise soda-lime glass containers. 
     
     
       9. The method of strengthening newlyformed soda-lime containers having surface defects in their exterior surfaces comprising the steps of allowing the said newly-formed glass containers to cool to a temperature ranging from about 800° to 1100° F. immediately following their formation, immediately rapidly heating the defect-bearing, newly-formed exterior surfaces of said containers to a temperature ranging from about 1000° to 1250° F. for a period of time of about 1 to 4 seconds, said time period being less than that which would cause visible softening or fusing of said glass surfaces, and then annealing said glass containers to remove stresses therefrom, at least some of said defects remaining visible in said defect-bearing exterior surfaces, thereby significantly strengthening said glass containers by about 10 to 50 percent greater than their original strength as indicated by internal pressure strength tests. 
     
     
       10. The method in accordance with claim 9, wherein the said defect-bearing exterior surfaces are subjected to direct flame for the stated period. 
     
     
       11. The method in accordance with claim 9, wherein the defect-bearing exterior surfaces of said glass containers are heated with direct flame from a gas-fired torch for the stated period. 
     
     
       12. The method of strengthening newly-formed soda-lime glass containers having surface defects in their exterior surfaces comprising the steps of allowing the said newly-formed glass containers to cool to a temperature ranging from about 800° to 1100° F. immediately following their formation, immediately rapidly heating the defect-bearing newly-formed exterior surfaces of said containers to a temperature ranging from about 1000° to 1250° F. for a period of time of about 1 to 6 minutes in an oven, said time period being less than that which would cause visible softening or melting of said glass surfaces, and then annealing said glass containers to remove stresses therefrom, at least some defects remaining visible in said defect-bearing exterior surfaces, thereby significantly strengthening said glass containers by about 10 to 50 percent greater than their original strength as indicated by internal pressure strength tests.